The present invention relates generally to drill bits, and more specifically relates to methods and apparatus for establishing a hydraulic flow regime proximate selected portions of a drill bit.
The use of drill bits for the drilling of wells in earth formations or for taking cores of formations is well known. Bits for either purpose may include either stationary cutting elements for cutting or abrading the earth formation, or cutting elements mounted on rotating cones. Bits as presently known to the industry which utilize stationary cutting elements typically use either natural or synthetic diamonds as cutting elements and are known as "diamond bits". References herein to "diamond bits" or "diamond drill bits" refer to all bits, for either drilling or coring, having primarily stationary cutters.
Conventional diamond drill bits include a solid body having a plurality of cutting elements, or "cutters" secured therein. As the bit is rotated in the formation, the cutters contact and cut the formation. Hydraulic flow through the bit is utilized to cool the cutters of the bit and to flush cuttings away from the cutters and to the annulus. An important consideration in the design of diamond bits is the hydraulic performance of the bit. In conventional diamond bit design, hydraulic flow will exit the bit generally proximate the center of the bit and will flow generally radially outwardly through channels formed between the cutter faces. In some designs nozzles are utilized to direct the hydraulic flow directly proximate specified cutters. The hydraulic flow path, however, remains in a generally radially outward direction.
While such conventional designs are widely used today, difficulties are still encountered in maintaining a hydraulic flow which will efficiently and effectively cool and clean each cutter in the bit. In conventional bits the cutters which are proximate the point at which fluid exits from the interior of the bit are more effectively cooled than are cutters which are more remote from such location. Significant efforts have been made to design nozzles which will direct an appropriate proportion of the hydraulic flow at selected cutters in the bit to assure adequate cooling and operation. Such conventional designs, while performing satisfactorily, may not provide optimal cooling for each cutter.
One prior art attempt to distribute hydraulic energy across the face of the bit to cool the cutting elements is disclosed in U.S. Pat. No. 4,655,303 to Winters, et al. U.S. Pat. No. 4,655,303 discloses a drill bit having a central aperture through which hydraulic flow will emanate, and a plurality of radial channels extending from such aperture. The depth of each of these radial channels decreases as each channel widens along its outward path. Additionally, the extension of the diamond cutters above the surface of the bit decreases as a function of radial distance from the center of the bit. The intended function of these two design factors is to maintain a constant flow area available to the hydraulic flow regime across the radius of the bit, so as to maintain an established uniform pressure and flow across the face of the bit. This general technique has been utilized for a substantial period of time in the industry.
This type of design inherently includes many deficiencies. The design is not suitable for use with certain, particularly larger, types of cutters. The design is not practical for bits having multiple sizes of cutters, and the design requires the sizing of the cutters in a manner which, while possibly improving the hydraulic flow characteristics of the bit, may restrict the bit design to cutters which are sized and distributed in a manner which is less than optimal for cutting certain formations.
Accordingly, the present invention provides a new method and apparatus for controlling the hydraulic flow in a diamond drill bit whereby portions of the flow may be distributed uniformly across groups of cutting elements, and which is practical for use with a variety of types and sizes of cutting elements.